Conventionally, a cathode ray tube has been used mainly as an image display apparatus for color television, personal computer and the like. However, in recent years, an image display apparatus has been required to be miniaturized, lightened and thinner. In order to satisfy these demands, various types of thin image display apparatus have been developed and commercialized.
Under these circumstances, various types of thin image display apparatus have been researched and developed recently. In particular, a liquid crystal display and a plasma display have been developed actively. The liquid crystal display has been applied to various types of products such as a portable computer, a portable television, a video camera, a car-navigation system and the like. In addition to that, the plasma display has been applied to a product such as a large-scale display, for example, 20 inch-display or 40-inch display.
However, there are the following problems for the liquid crystal display and the plasma display. The liquid crystal display has a narrow visual angle and a slow response. Regarding the plasma display, high brightness can't be obtained and the consumed electricity is large.
Then, an image display apparatus (hereinafter referred to as "a field emission display", or "a display") to which field emission, that is, a phenomenon in which electrons are emitted in a vacuum at room temperature, is applied, has attracted considerable attention. The field emission display is a spontaneous luminescent type, therefore it is possible to obtain a wide visual angle and high brightness. Further, its basic principle (to illuminate a fluorescent substance with electron beams) is same as that of a conventional cathode ray tube, and therefore a picture with natural color and high reproduction can be displayed.
The above-mentioned type of field emission display is disclosed in Japanese Laid Open Patent No. (Tokkai-Sho) 61-221783, Japanese Laid Open Patent No. (Tokkai-Hei) 1-100842, and Japanese Laid Open Patent No. (Tokkai-Hei) 2-61946.
FIG. 7 is a cross-sectional view showing schematic structure of a first conventional field emission display (refer to Japanese Laid Open Patent No. (Tokkai-Sho) 61-221783). As shown in FIG. 7, the conventional field emission display comprises an electron emission source 21, a transparent flat substrate 24, a fluorescent layer 23 and a conductive thin film 25. The fluorescent layer 23 and the conductive thin film 25 are layered sequentially on the inner surface of the transparent flat substrate 24 and face the electron emission source 21. The cathode (electron emission source) 21 comprises a plurality of conductive micro-points 21a formed on the surface of a conductive coating material 21b and the conductive coating material 21b is layered on the surface of an insulating substrate 21c. Each conductive micro-point 21a is separated by an insulating coating material 21d. A grid 21e, in which a hole is provided at the position corresponding to each conductive micro-point 21a, is provided on the insulating coating material 21d.
According to the above-mentioned field emission display, conductive micro-points 21a emit electrons to excite the fluorescent layer 23. The excited fluorescent layer 23 emits a light and the light is observed through a transparent flat substrate 24. According to the conventional technique, it is required to form 20,000 to 30,000 pieces of conductive micro-points 21a per square-millimeter and electrons (electron beams) are emitted from a plurality of conductive micro-points 21a to illuminate one pixel.
FIG. 8 is a cross-sectional view showing schematic structure of a second conventional field emission display (refer to Japanese Laid Open Patent No. (Tokkai-Hei) 2-61946). As shown in FIG. 8, the conventional field emission display comprises an electron emission source 31, a fluorescent layer 33a, 33b and 33c, a transparent flat substrate 34, and a conductive thin film 35a, 35b and 35c. The fluorescent layers, 33a, 33b and 33c, and the conductive thin films 35a, 35b and 35c are layered sequentially on the inner surface of the transparent flat substrate 34 and face the electron emission source 31. The electron emission source 31 comprises a plurality of conductive micro-points 31a formed on a conductive coating material 31b, and the conductive coating material 31b is layered on the surface of an insulating substrate 31c. Each conductive micro-point 31a is separated by an insulating coating material 31d. A grid 31e is provided on the insulating coating material 31d.
According to the above-mentioned field emission display, electrons which are emitted from a plurality of conductive micro-points 31a can be landed at intended components of the fluorescent layer (in FIG. 8, a fluorescent layer 33a) by controlling a potential which is applied to the conductive thin films 35.
FIG. 9 is a cross-sectional view showing schematic structure of a third conventional field emission display (refer to Japanese Laid Open Patent No. (Tokkai-Hei) 1-100842). As shown in FIG. 9, the conventional field emission display comprises an electron emission source 41, a fluorescent layer 43a and 43b, a faceplate 44 and a transparent electrode 45. The fluorescent layers 43a and 43b are provided on the faceplate 44 via the transparent electrode 45. The electron emission source 41 faces the fluorescent layers 43a and 43b. The electron emission source 41 comprises a substrate 41e, a thin film 41c formed on the substrate 41e and electrodes 41a and 41b which are provided for applying a voltage to the thin film 41c. An electron emission part 41d is provided by processing the thin film 41c.
According to the above-mentioned field emission display, the deflection of electron beams emitted from the electron emission part 41d is controlled by controlling a voltage applied to electrodes 41a and 41b, and the deflected electron beam excites a fluorescent layer 43a or 43b, and the fluorescent layer 43a or 43b is illuminated. Further, in the conventional field emission display, a technology such that electron beams are focused on the surface of the fluorescent layer by providing a flat electrode (not shown in FIG. 9) between the electron emission source 41 and the fluorescent layer 43 and applying a voltage lower than that of a transparent electrode 45 to the flat electrode, is used, that is, the technology such that the electron beams are focused on the surface of the fluorescent layer by utilizing the lens effect, is used.
However, the conventional field emission display shown in FIG. 7 has following problems. Electrons which are emitted from a conductive micro-point 21a are very weak, therefore a fluorescent layer 23 and an electron emission source 21 are required to face each other very closely. Further, it is required that one pixel of fluorescent substance is illuminated by electrons which are emitted from a plurality of conductive micro-points 21a, and therefore electron beams can't be deflected and focused. As a result, electrons which land on the fluorescent layer 23 extend, and therefore it is difficult to increase the density of the fluorescent layer 23. Consequently, a display having high resolution can't be provided.
In the conventional field emission display shown in FIG. 8, electron beams are deflected by controlling (switching) a potential which is applied to a conductive thin film 35. In order to switch the conducive thin film 35, it is required that a switching scan be performed under a high voltage. However, it is very difficult to realize a circuit element in which a high voltage of kilo volt order applied to the conductive thin film 35 can be switched at a high frequency in an image display. Consequently, according to the conventional technology, a display having high resolution can't be provided.
In the conventional field emission display shown in FIG. 9, the electron beams are deflected and focused. However, in the conventional field emission display, a current is passed between two electrodes 41a and 41b to generate electrons, and the character, such that emitted electron beams are always deflected by the potential difference between electrodes, is used. Consequently, the potential difference between these two electrodes 41a and 41b is required to be a predetermined value to emit electron beams. Therefore the direction of deflection can be changed but a desirable voltage to control the grade of the deflection can't be applied. Regarding focusing of electron beams, the electron beams are focused by controlling a voltage which is applied to a flat electrode. However, the flat electrode has only one function for changing the direction of electron beams that are emitted with a certain angle to predetermined directions. Consequently, according to the conventional field emission display, scanning deflection, that is, where an angle of electron beams are changed appropriately for the electron beams to land on a plurality of pixels of the fluorescent substance sequentially, can't be performed.
Further, in the conventional field emission displays shown in FIGS. 7, 8 and 9, if a deviation of position between an electron emission source 21, 31 and 41, and a fluorescent layer 23, 33 and 43, respectively, (a deviation of position caused by manufacturing error or assembling error of each material and the like) is caused, there is no function for adjusting the deviation of position. Consequently, electron beams can't be prevented from irradiating a fluorescent substance other than a desired fluorescent substance. As a result, it is required to have a predetermined tolerance in designing a fluorescent pixel and an electron emission source, and therefore it is difficult to provide a display having high resolution.